10:15 〜 10:30
[SVC33-06] 軸対称に広がる粘性流体の温度変化：溶岩ドーム熱観測への示唆
キーワード：溶岩流、熱観測、粘性流体、重力流
Lava flows are high-temperature gravity currents that propagate along the surface and eventually solidify due to radiative cooling. Radiative intensity is a key observable in satellite monitoring, as it strongly correlates with the effusion rate. Although observations have shown that the proportionality coefficient between radiative intensity and effusion rate is highly dependent on lava composition (Coppola et al., 2013), the underlying mechanism remains unclear. In this study, we theoretically investigate how radiative intensity varies with lava viscosity using a depth-averaged model that describes the dynamics of flow and cooling.
We consider a lava flow spreading radially over a flat plane, where lava is supplied at a constant rate from a point source. The lava is assumed to behave as a Newtonian fluid. Radiative and convective cooling at the surface, as well as internal heat conduction, are accounted for, while rheological changes due to temperature variations are neglected. As cooling progresses, the flow develops a cold surface layer that covers a hotter interior layer. We numerically solve the energy conservation equation for heat loss in the cold layer along with the mass conservation equation for flow thickness. This model can describe the evolution of the vertical temperature distribution.
We tested our model against analogue experiments using silicone oil conducted by Garel et al. (2012). Our model successfully reproduced the surface temperature distribution observed in the experiments: approximately 40°C near the source and around 20°C in the outer region. Additionally, our model revealed that the silicone oil maintained an almost uniform vertical temperature due to effective heat conduction. A dimensional analysis under the assumption of vertical uniformity indicates that, in steady-state conditions, radiative intensity is linearly proportional to the effusion rate but independent of viscosity. In contrast, the relaxation time required to reach steady state is proportional to the one-fourth power of the product of effusion rate and viscosity. In this talk, we report our analysis to higher temperatures and larger-scale conditions relevant to natural lava flows and demonstrate that steady-state radiative intensity can depend on viscosity due to vertical temperature non-uniformity.
We consider a lava flow spreading radially over a flat plane, where lava is supplied at a constant rate from a point source. The lava is assumed to behave as a Newtonian fluid. Radiative and convective cooling at the surface, as well as internal heat conduction, are accounted for, while rheological changes due to temperature variations are neglected. As cooling progresses, the flow develops a cold surface layer that covers a hotter interior layer. We numerically solve the energy conservation equation for heat loss in the cold layer along with the mass conservation equation for flow thickness. This model can describe the evolution of the vertical temperature distribution.
We tested our model against analogue experiments using silicone oil conducted by Garel et al. (2012). Our model successfully reproduced the surface temperature distribution observed in the experiments: approximately 40°C near the source and around 20°C in the outer region. Additionally, our model revealed that the silicone oil maintained an almost uniform vertical temperature due to effective heat conduction. A dimensional analysis under the assumption of vertical uniformity indicates that, in steady-state conditions, radiative intensity is linearly proportional to the effusion rate but independent of viscosity. In contrast, the relaxation time required to reach steady state is proportional to the one-fourth power of the product of effusion rate and viscosity. In this talk, we report our analysis to higher temperatures and larger-scale conditions relevant to natural lava flows and demonstrate that steady-state radiative intensity can depend on viscosity due to vertical temperature non-uniformity.